Association in alcoholic patients between Psychopathic Traits and the additive effect of allelic forms of theCNR1 andFAAH endocannabinoid genes, and the 3′ Region of theDRD2 Gene

The neurobiology of antisocial personality disorder

Despite increasing recognition that there is a neurobiological basis of antisocial behavior in addition to its psychosocial foundation, much less is known about the specificity of the neurobiological findings to the psychiatric condition of antisocial personality disorder (APD). This article provides a review of research on genetic, brain imaging, neurocognitive, and psychophysiological factors in relation to assessments of APD. Findings show that there are significant genetic effects on APD, particularly related to the serotonergic system, as well as abnormalities in brain regions such as the frontal lobe. Associations between psychophysiological measures of autonomic nervous system functioning and APD are more mixed. Results indicating that APD has a significant genetic basis and is characterized by abnormalities in brain structure/function and neurocognitive impairments provide additional evidence that supports the conceptualization of APD as a neurodevelopmental disorder. Findings may also help inform treatment approaches that target neurobiological risks for APD symptoms. This article is part of the Special Issue on "Personality Disorders".

Beyond monoamines: II. Novel applications for PET imaging in psychiatric disorders

Early applications of positron emission tomography (PET) in psychiatry sought to identify derangements of cerebral blood flow and metabolism. The need for more specific neurochemical imaging probes was soon evident, and these probes initially targeted the sites of action of neuroleptic (dopamine D₂ receptors) and psychoactive (serotonin receptors) drugs. For nearly 30 years, the centrality of monoamine dysfunction in psychiatric disorders drove the development of an armamentarium of monoaminergic PET radiopharmaceuticals and imaging methodologies. However, continued investments in monoamine-enhancing drug development realized only modest gains in efficacy and tolerability. As patent protection for many widely prescribed and profitable psychiatric drugs lapsed, drug development pipelines shifted away from monoamines in search of novel targets with the promises of improved efficacy, or abandoned altogether. Over this period, PET radiopharmaceutical development activities closely parallelled drug development priorities, resulting in the development of new PET imaging agents for non-monoamine targets. In part two of this review, we survey clinical research studies using the novel targets and radiotracers described in part one across major psychiatric application areas such as substance use disorders, anxiety disorders, eating disorders, personality disorders, mood disorders, and schizophrenia. Important limitations of the studies described are discussed, as well as key methodologic issues, challenges to the field, and the status of clinical trials seeking to exploit these targets for novel therapeutics.

Biomarkers of the Endocannabinoid System in Substance Use Disorders

Despite substance use disorders (SUD) being one of the leading causes of disability and mortality globally, available therapeutic approaches remain ineffective. The difficulty in accurately characterizing the neurobiological mechanisms involved with a purely qualitative diagnosis is an obstacle to improving the classification and treatment of SUD. In this regard, identifying central and peripheral biomarkers is essential to diagnosing the severity of drug dependence, monitoring therapeutic efficacy, predicting treatment response, and enhancing the development of safer and more effective pharmacological tools. In recent years, the crucial role that the endocannabinoid system (ECS) plays in regulating the reinforcing and motivational properties of drugs of abuse has been described. This has led to studies characterizing ECS alterations after exposure to various substances to identify biomarkers with potential diagnostic, prognostic, or therapeutic utility. This review aims to compile the primary evidence available from rodent and clinical studies on how the ECS components are modified in the context of different substance-related disorders, gathering data from genetic, molecular, functional, and neuroimaging experimental approaches. Finally, this report concludes that additional translational research is needed to further characterize the modifications of the ECS in the context of SUD, and their potential usefulness in the necessary search for biomarkers.

The endocannabinoid system in borderline personality disorder and antisocial personality disorder: A scoping review

Individuals with borderline personality disorder (BPD) or antisocial personality disorder (ASPD) are overrepresented in forensic settings. Yet, despite the burden these disorders place on healthcare and criminal justice systems, there remains a lack of evidence-based pharmacological treatments. Epidemiological data have shown that comorbid cannabis use disorders are common in BPD and ASPD. ∆⁹ -Tetrahydrocannabinol, the primary psychoactive constituent of cannabis, is an exogenous cannabinoid that stimulates the endocannabinoid system (ECS). Hence, an investigation of the ECS in these conditions is warranted. This scoping review screened 105 records and summarized the extant research on the ECS in ASPD (n = 69) and BPD (n = 61) participants. Preliminary results suggest that alterations of the ECS may be present in these disorders. Although research examining the ECS in personality disorders is still in its infancy, more research is warranted given initial positive findings.

Lower amygdala fatty acid amide hydrolase in violent offenders with antisocial personality disorder: an [11C]CURB positron emission tomography study

Antisocial personality disorder (ASPD) imposes a high societal burden given the repetitive reactive aggression that affected individuals perpetrate. Since the brain endocannabinoid system (ECS) has been implicated in ASPD and aggressive behavior, we utilized [¹¹C]CURB positron emission tomography to investigate fatty acid amide hydrolase (FAAH), an enzyme of the ECS that degrades anandamide, in 16 individuals with ASPD and 16 control participants. We hypothesized that FAAH density would be lower in the amygdala for several reasons. First, decreased FAAH expression is associated with increased cannabinoid receptor 1 stimulation, which may be responsible for amygdala hyper-reactivity in reactive aggression. Second, the amygdala is the seat of the neural circuit mediating reactive aggression. Third, other PET studies of externalizing populations show reduced brain FAAH density. Conversely, we hypothesized that FAAH expression would be greater in the orbitofrontal cortex. Consistent with our hypothesis, we found that amygdala FAAH density was lower in the amygdala of ASPD (p = 0.013). Cerebellar and striatal FAAH expression were inversely related with impulsivity (cerebellum: r = -0.60, p = 0.017; dorsal caudate: r = -0.58, p = 0.023; dorsal putamen: r = -0.55, p = 0.034), while cerebellar FAAH density was also negatively associated with assaultive aggression (r = -0.54, p = 0.035). ASPD presents high levels of disruptive behavior with few, if any, efficacious treatment options. Novel therapeutics that increase FAAH brain levels in a region-specific manner could hold promise for attenuating certain symptom clusters of ASPD, although our results require replication.

Association of ANKK1 polymorphism with antipsychotic-induced hyperprolactinemia

OBJECTIVE

Schizophrenia is a severe highly heritable mental disorder. Genetic polymorphisms of dopaminergic pathways are related to pathogenesis of drug response. Hyperprolactinemia (HPRL), a common adverse effect of antipsychotics, is attributed to blockade of dopamine D2 receptors. Ankyrin Repeat and Kinase Domain containing 1 (ANKK1) gene is closely related to Dopamine Receptor D2 type (DRD2) gene functioning. We examined whether the functional polymorphism rs2734849 in the ANKK1 gene is associated with antipsychotic-induced HPRL.

METHODS

We recruited 446 patients with schizophrenia from among the Russian population of the Siberian region. The polymorphism rs2734849 in the ANKK1 gene was genotyped with The MassARRAY® Analyzer 4 by Agena Bioscience™, using the kit SEQUENOM Consumables iPLEXGold 384. Genotype and allele frequencies were compared between groups of schizophrenia patients with and without HPRL using the χ² test.

RESULTS

A comparison between schizophrenia patients with and without HPRL revealed significantly higher frequency of the C allele of the polymorphic variant rs2734849 in the ANKK1 gene in patients with HPRL as compared to the patients without it (χ² = 3.70; p = .05; odds ratio [OR] = 1.30 [0.99-1.69]).

CONCLUSION

The functional polymorphism rs2734849 in the ANKK1 gene was associated with HPRL in patients with schizophrenia.

Born this way? A review of neurobiological and environmental evidence for the etiology of psychopathy

Across a significant body of research, psychopathy has often been conceptualized as a biologically based malady. In this research, genetic and neurobiological differences have been conceptualized to underlie psychopathy, while affected individuals' life experiences only influence expressed psychopathic features and their severity. Psychopathy research has largely ignored developmental evidence demonstrating significant influences of environment on both biological and behavioral processes, resulting in several prominent criticisms (Edens & Vincent, 2008; Loeber, Byrd, & Farrington, 2015). The current review was conducted with two main aims: (a) to collect and consider etiological evidence from the extant body of research on genetic and neurobiological factors in psychopathy; and (b) to evaluate findings from genetic, neurotransmitter, brain structure, and brain function studies in the context of relevant evidence from developmental research. Examples from research on adversity and traumatic stress, a common correlate of psychopathy, were used to highlight current research gaps and future directions to aid in the integration of developmental and neurobiological research agendas. While some promising evidence exists regarding possible underlying neurobiological processes of psychopathic traits, this evidence is insufficient to suggest a largely biological etiology for the disorder. Further, information from developmental and epigenetic research may suggest complex, multidimensional trajectories for individuals experiencing psychopathy. Based on these observations, the authors make several recommendations for future research, as well as for current clinical application and practice.

Biomarkers in aggression

Aggressive behavior exerts an enormous impact on society remaining among the main causes of worldwide premature death. Effective primary interventions, relying on predictive models of aggression that show adequate sensitivity and specificity are currently lacking. One strategy to increase the accuracy and precision of prediction would be to include biological data in the predictive models. Clearly, to be included in such models, biological markers should be reliably associated with the specific trait under study (i.e., diagnostic biomarkers). Aggression, however, is phenotypically highly heterogeneous, an element that has hindered the identification of reliable biomarkers. However, current research is trying to overcome these challenges by focusing on more homogenous aggression subtypes and/or by studying large sample size of aggressive individuals. Further advance is coming by bioinformatics approaches that are allowing the integration of inter-species biological data as well as the development of predictive algorithms able to discriminate subjects on the basis of the propensity toward aggressive behavior. In this review we first present a brief summary of the available evidence on neuroimaging of aggression. We will then treat extensively the data on genetic determinants, including those from hypothesis-free genome-wide association studies (GWAS) and candidate gene studies. Transcriptomic and neurochemical biomarkers will then be reviewed, and we will dedicate a section on the role of metabolomics in aggression. Finally, we will discuss how biomarkers can inform the development of new pharmacological tools as well as increase the efficacy of preventive strategies.

Evaluation of association of DRD2 TaqIA and -141C InsDel polymorphisms with food intake and anthropometric data in children at the first stages of development

The reward sensation after food intake may be different between individuals and variants in genes related to the dopaminergic system may indicate a different response in people exposed to the same environmental factors. This study investigated the association of TaqIA (rs1800497) and -141C InsDel (rs1799732) variants in DRD2/ANKK1 gene with food intake and adiposity parameters in a cohort of children. The sample consisted of 270 children followed until 7 to 8 years old. DNA was extracted from blood and polymorphisms were detected by PCR-RFLP analysis. Food intake and nutritional status were compared among individuals with different SNP genotypes. Children carrying the A1 allele (TaqIA) had higher energy of lipid dense foods (LDF) when compared with A2/A2 homozygous children at 7 to 8 years old (GLM p=0.004; Mann Whitney p=0.005). No association was detected with -141C Ins/Del polymorphism. To our knowledge, this is the first association study of the DRD2 TaqIA and -141C Ins/Del polymorphism with food intake and anthropometric parameters in children. DRD2 TaqIA polymorphism has been associated with a reduction in D₂ dopamine receptor availability. Therefore, the differences observed in LDF intake in our sample may occur as an effort to compensate the hypodopaminergic functioning.

The Endocannabinoid System, Aggression, and the Violence of Synthetic Cannabinoid Use, Borderline Personality Disorder, Antisocial Personality Disorder, and Other Psychiatric Disorders

Endogenous and exogenous cannabinoids bind to central cannabinoid receptors to control a multitude of behavioral functions, including aggression. The first main objective of this review is to dissect components of the endocannabinoid system, including cannabinoid 1 and cannabinoid 2 receptors; the endogenous cannabinoids anandamide and 2-arachidonoylglycerol; and the indirect cannabinoid modulators fatty acid amide hydrolase and monoacylglycerol lipase; that have shown abnormalities in basic research studies investigating mechanisms of aggression. While most human research has concluded that the active ingredient of marijuana, Δ9-tetrahydrocannabinol, tends to dampen rather than provoke aggression in acute doses, recent evidence supports a relationship between the ingestion of synthetic cannabinoids and emergence of violent or aggressive behavior. Thus, another objective is to evaluate the emerging clinical data. This paper also discusses the relationship between prenatal and perinatal exposure to cannabis as well as use of cannabis in adolescence on aggressive outcomes. A final objective of the paper is to discuss endocannabinoid abnormalities in psychotic and affective disorders, as well as clinically aggressive populations, such as borderline personality disorder and antisocial personality disorder. With regard to the former condition, decreased anandamide metabolites have been reported in the cerebrospinal fluid, while some preliminary evidence suggests that fatty acid amide hydrolase genetic polymorphisms are linked to antisocial personality disorder and impulsive-antisocial psychopathic traits. To summarize, this paper will draw upon basic and clinical research to explain how the endocannabinoid system may contribute to the genesis of aggressive behavior.

Involvement of Endocannabinoids in Alcohol "Binge" Drinking: Studies of Mice with Human Fatty Acid Amide Hydrolase Genetic Variation and After CB1 Receptor Antagonists

BACKGROUND

The endocannabinoid system has been found to play an important role in modulating alcohol intake. Inhibition or genetic deletion of fatty acid amide hydrolase (FAAH; a key catabolic enzyme for endocannabinoids) leads to increased alcohol consumption and preference in rodent models. A common human single-nucleotide polymorphism (SNP; C385A, rs324420) in the FAAH gene is associated with decreased enzymatic activity of FAAH, resulting in increased anandamide levels in both humans and FAAH C385A knock-in mice.

METHODS

As this FAAH SNP has been reported to be associated with altered alcohol abuse, the present study used these genetic knock-in mice containing the human SNP C385A to determine the impact of variant FAAH gene on alcohol "binge" drinking in the drinking-in-the-dark (DID) model.

RESULTS

We found that the FAAH(A/A) mice had greater alcohol intake and preference than the wild-type FAAH(C/C) mice, suggesting that increased endocannabinoid signaling in FAAH(A/A) mice led to increased alcohol "binge" consumption. The specificity on alcohol vulnerability was suggested by the lack of any FAAH genotype difference on sucrose or saccharin intake. Using the "binge" DID model, we confirmed that selective CB1 receptor antagonist AM251 reduced alcohol intake in the wild-type mice.

CONCLUSIONS

These data suggest that there is direct and selective involvement of the human FAAH C385A SNP and CB1 receptors in alcohol "binge" drinking.

Mesocorticolimbic dopamine functioning in primary psychopathy: A source of within-group heterogeneity

Despite similar emotional deficiencies, primary psychopathic individuals can be situated on a continuum that spans from controlled to disinhibited. The constructs on which primary psychopaths are found to diverge, such as self-control, cognitive flexibility, and executive functioning, are crucially regulated by dopamine (DA). As such, the goal of this review is to examine which specific alterations in the meso-cortico-limbic DA system and corresponding genes (e.g., TH, DAT, COMT, DRD2, DRD4) might bias development towards a more controlled or disinhibited expression of primary psychopathy. Based on empirical data, it is argued that primary psychopathy is generally related to a higher tonic and population activity of striatal DA neurons and lower levels of D2-type DA receptors in meso-cortico-limbic projections, which may boost motivational drive towards incentive-laden goals, dampen punishment sensitivity, and increase future reward-expectancy. However, increasingly higher levels of DA activity in the striatum (moderate versus pathological elevations), lower levels of DA functionality in the prefrontal cortex, and higher D1-to-D2-type receptor ratios in meso-cortico-limbic projections may lead to increasingly disinhibited and impetuous phenotypes of primary psychopathy. Finally, in order to provide a more coherent view on etiological mechanisms, we discuss interactions between DA and serotonin that are relevant for primary psychopathy.

Common single nucleotide variants underlying drug addiction: more than a decade of research

Drug-related phenotypes are common complex and highly heritable traits. In the last few years, candidate gene (CGAS) and genome-wide association studies (GWAS) have identified a huge number of single nucleotide polymorphisms (SNPs) associated with drug use, abuse or dependence, mainly related to alcohol or nicotine. Nevertheless, few of these associations have been replicated in independent studies. The aim of this study was to provide a review of the SNPs that have been most significantly associated with alcohol-, nicotine-, cannabis- and cocaine-related phenotypes in humans between the years of 2000 and 2012. To this end, we selected CGAS, GWAS, family-based association and case-only studies published in peer-reviewed international scientific journals (using the PubMed/MEDLINE and Addiction GWAS Resource databases) in which a significant association was reported. A total of 371 studies fit the search criteria. We then filtered SNPs with at least one replication study and performed meta-analysis of the significance of the associations. SNPs in the alcohol metabolizing genes, in the cholinergic gene cluster CHRNA5-CHRNA3-CHRNB4, and in the DRD2 and ANNK1 genes, are, to date, the most replicated and significant gene variants associated with alcohol- and nicotine-related phenotypes. In the case of cannabis and cocaine, a far fewer number of studies and replications have been reported, indicating either a need for further investigation or that the genetics of cannabis/cocaine addiction are more elusive. This review brings a global state-of-the-art vision of the behavioral genetics of addiction and collaborates on formulation of new hypothesis to guide future work.

The Addiction-Related Gene Ankk1 is Oppositely Regulated by D1R- and D2R-Like Dopamine Receptors

The ankyrin repeat and kinase domain containing 1 (ANKK1) TaqIA polymorphism has been extensively studied as a marker of the gene for dopamine receptor D2 (DRD2) in addictions and other dopamine-associated traits. In vitro mRNA and protein studies have shown a potential connection between ANKK1 and the dopaminergic system functioning. Here, we have investigated whether Ankk1 expression in the brain is regulated by treatment with dopaminergic agonists. We used quantitative RT-PCR of total brain and Western blots of specific brain areas to study Ankk1 in murine brain after dopaminergic treatments. We found that Ankk1 mRNA was upregulated after activation of D1R-like dopamine receptors with SKF38393 (2.660 ± 1.035-fold; t: 4.066, df: 11, P = 0.002) and apomorphine (2.043 ± 0.595-fold; t: 3.782, df: 8, P = 0.005). The D2R-like agonist quinelorane has no effect upon Ankk1 mRNA (1.004 ± 0.580-fold; t: 0.015, df: 10, P = 0.9885). In contrast, mice treatment with the D2R-like agonists 7-OH-DPAT and aripiprazole caused a significant Ankk1 mRNA downregulation (0.606 ± 0.057-fold; t: 2.786, df: 10, P = 0.02 and 0.588 ± 0.130-fold; t: 2.394, df: 11, P = 0.036, respectively). With respect the Ankk1 proteins profile, no effects were found after SKF38393 (t: 0.54, df: 2, P = 0.643) and Quinelorane (t: 0.286, df: 8, P = 0.782) treatments. In contrast, the D2R-like agonist 7-OH-DPAT (±) caused a significant increment of Ankk1 in the striatum (t: 2.718, df: 7; P = 0.03) when compared to the prefrontal cortex. The activation of D1R-like and D2-R-like leads to opposite transcriptional regulation of Ankk1 by specific pathways.

Hypothesizing dopaminergic genetic antecedents in schizophrenia and substance seeking behavior

The dopamine system has been implicated in both substance use disorder (SUD) and schizophrenia. A recent meta-analysis suggests that A1 allele of the DRD2 gene imposes genetic risk for SUD, especially alcoholism and has been implicated in Reward Deficiency Syndrome (RDS). We hypothesize that dopamine D2 receptor (DRD2) gene Taq1 A2 allele is associated with a subtype of non-SUD schizophrenics and as such may act as a putative protective agent against the development of addiction to alcohol or other drugs of abuse. Schizophrenics with SUD may be carriers of the DRD2 Taq1 A1 allele, and/or other RDS reward polymorphisms and have hypodopaminergic reward function. One plausible mechanism for alcohol seeking in schizophrenics with SUD, based on previous research, may be a deficiency of gamma type endorphins that has been linked to schizophrenic type psychosis. We also propose that alcohol seeking behavior in schizophrenics, may serve as a physiological self-healing process linked to the increased function of the gamma endorphins, thereby reducing abnormal dopaminergic activity at the nucleus accumbens (NAc). These hypotheses warrant further investigation and cautious interpretation. We, therefore, encourage research involving neuroimaging, genome wide association studies (GWAS), and epigenetic investigation into the relationship between neurogenetics and systems biology to unravel the role of dopamine in psychiatric illness and SUD.

The neuropsychological contributors to psychopathic personality traits in adolescence

Research has consistently revealed that measures of psychopathy and psychopathic personality traits represent some of the most consistent predictors of violent criminal involvement. As a result, there has been a considerable amount of interest in trying to identify the various etiological factors related to psychopathy. The current study builds on this existing body of literature by examining the association between neuropsychological deficits and psychopathic personality traits. Data from the National Institute of Child Health and Human Development (NICHD) Study of Early Child Care were analyzed. Adolescent psychopathic personality traits were measured with a 15-item scale drawn from the Youth Psychopathic Traits Inventory (YPI), whereas neuropsychological functioning was assessed with a number of standardized tests of cognitive skills. Analyses revealed that neuropsychological deficits were significantly related to psychopathy measures across all four measurement phases. Neuropsychological deficits also predicted scoring in the top 5% of psychopathic personality traits.

A review of the interactions between alcohol and the endocannabinoid system: implications for alcohol dependence and future directions for research

Over the past fifty years a significant body of evidence has been compiled suggesting an interaction between the endocannabinoid (EC) system and alcohol dependence. However, much of this work has been conducted only in the past two decades following the elucidation of the molecular constituents of the EC system that began with the serendipitous discovery of the cannabinoid 1 receptor (CB1). Since then, novel pharmacological and genetic tools have enabled researchers to manipulate select components of the EC system, to determine their contribution to the motivation to consume ethanol. From these preclinical studies, it is evident that CB1 contributes the motivational and reinforcing properties of ethanol, and chronic consumption of ethanol alters EC transmitter levels and CB1 expression in brain nuclei associated with addiction pathways. These results are augmented by in vitro and ex vivo studies showing that acute and chronic treatment with ethanol produces physiologically relevant alterations in the function of the EC system. This report provides a current and comprehensive review of the literature regarding the interactions between ethanol and the EC system. We begin be reviewing the studies published prior to the discovery of the EC system that compared the behavioral and physiological effects of cannabinoids with ethanol in addition to cross-tolerance between these drugs. Next, a brief overview of the molecular constituents of the EC system is provided as context for the subsequent review of more recent studies examining the interaction of ethanol with the EC system. These results are compiled into a summary providing a scheme for the known changes to the components of the EC system in different stages of alcohol dependence. Finally, future directions for research are discussed.

Association Study of Two Cannabinoid Receptor Genes, CNR1 and CNR2, with Methamphetamine Dependence

Several studies have suggested that the endocannabinoid system plays significant roles in the vulnerability to psychiatric disorders including drug abuse. To examine the possible association of the CNR1 and CNR2 genes, which encode cannabinoid receptors CB1 and CB2, with methamphetamine dependence, we investigated three single nucleotide polymorphisms (SNPs) (rs806379, rs1535255, rs2023239) in intron 2 of the CNR1 gene and a nonsynonymous SNP, Q63R, in the CNR2 gene. The study samples consisted of 223 patients with methamphetamine dependence and 292 age- and sex- matched controls. There were no significant differences between the patients and controls in genotypic or allelic distribution of any SNP of the CNR1 and CNR2 genes. We also analyzed the clinical features of methamphetamine dependence. Rs806379 of the CNR1 gene showed a significant association with the phenotype of latency of psychosis after the first consumption of methamphetamine. Patients with the T allele or T-positive genotypes (T/T or A/T) may develop a rapid onset of psychosis after methamphetamine abuse. The present study suggests a possibility that genetic variants of the CNR1 gene may produce a liability to the complication of psychotic state after abuse of methamphetamine; however, our findings need to be confirmed by future replications.

Genetic and environmental influences on psychiatric comorbidity: a systematic review

BACKGROUND

The purpose of this review is to systematically appraise the peer-reviewed literature about the genetic and environmental determinants of psychiatric comorbidity, focusing on four of the most prevalent types of psychopathology: anxiety disorders, depression, conduct disorder and substance abuse.

METHODS

We summarize existing empirical research on the relative contribution that genetic, nonshared and shared environmental factors make to the covariance between disorders, and evidence about specific genes and environmental characteristics that are associated with comorbidity.

RESULTS

Ninety-four articles met the inclusion criteria and were assessed. Genetic factors play a particularly strong role in comorbidity between major depression and generalized anxiety disorder or posttraumatic stress disorder, while the non-shared environments make an important contribution to comorbidity in affective disorders. Genetic and non-shared environmental factors also make a moderate-to-strong contribution to the relationship between CD and SA. A range of candidate genes, such as 5HTTLPR, MAOA, and DRD1-DRD4, as well as others implicated in the central nervous system, has been implicated in psychiatric comorbidity. Pivotal social factors include childhood adversity/life events, family and peer social connections, and socioeconomic and academic difficulties.

LIMITATIONS

Methodological concerns include the use of clinical case-control samples, the focus on a restricted set of individual-level environmental risk factors, and restricted follow-up times.

CONCLUSIONS

Given the significant mental health burden associated with comorbid disorders, population-based research on modifiable risk factors for psychiatric comorbidity is vital for the design of effective preventive and clinical interventions.

In search of genes associated with risk for psychopathic tendencies in children: a two-stage genome-wide association study of pooled DNA

BACKGROUND

Quantitative genetic data from our group indicates that antisocial behaviour (AB) is strongly heritable when coupled with psychopathic, callous-unemotional (CU) personality traits. We have also demonstrated that the genetic influences for AB and CU overlap considerably. We conducted a genome-wide association scan that capitalises on these findings in an attempt to identify quantitative trait loci (QTLs) that may increase risk for psychopathic tendencies (AB+/CU+).

METHODS

Teacher ratings at age 7 were used to screen 8374 twins with available DNA samples for individuals that were high vs. low on both AB and CU. In Stage 1, we screened for allele frequency differences in 642,432 autosomal single-nucleotide polymorphisms (SNPs) using the Affymetrix 6.0 GeneChip with pooled DNA for high-scoring (AB+/CU+) versus low-scoring children (N = approximately 300/group). In Stage 2, we tested the 3000 most strongly associated SNPs from Stage 1 for association in the same direction in a second sample of high- versus low-scoring children from the same twin study (18% co-twins).

RESULTS

Using allele frequencies estimated from pooled DNA, we found suggestive evidence for enrichment of association in the second stage of our two-stage genome-wide association design and focus on reporting the 30 top-ranking SNPs nominally associated with psychopathic tendencies. These SNPs include neurodevelopmental genes such as ROBO2.

CONCLUSIONS

Although none of the SNPs reached genome-wide statistical significance we have generated a list of SNPs that are potentially associated with psychopathic tendencies, which we believe warrant verification and replication in large independent and clinical samples.

Behavioral genetics in antisocial spectrum disorders and psychopathy: a review of the recent literature

Behavioral geneticists are increasingly using the tools of molecular genetics to extend upon discoveries from twin, family, and adoption studies concerning the heritability of antisocial spectrum disorders and psychopathy. While there is a substantial body of research concerning antisocial spectrum disorders in the behavioral genetics literature, only a few studies could be located using the phenotype of psychopathy. In this report we summarize some of the recent molecular genetics work concerning antisocial spectrum disorders and psychopathy, with a focus on genes involved in the serotonergic and dopaminergic pathways, while also mentioning some of the novel genetic factors being considered. Monoamine oxidase (MAOA) and the serotonin transporter (5HTT) are reviewed at length, as these genes have received significant scientific attention in recent years and are sites of high biological plausibility in antisocial spectrum disorders and psychopathy.

The ANKK1 gene associated with addictions is expressed in astroglial cells and upregulated by apomorphine

BACKGROUND

TaqIA, the most widely analyzed genetic polymorphism in addictions, has traditionally been considered a gene marker for association with D2 dopamine receptor gene (DRD2). TaqIA is located in the coding region of the ANKK1 gene that overlaps DRD2 and encodes a predicted kinase ANKK1. The ANKK1 protein nonetheless had yet to be identified. This study examined the ANKK1 expression pattern as a first step to uncover the biological bases of TaqIA-associated phenotypes.

METHODS

Northern blot and quantitative reverse-transcriptase polymerase chain reaction analyses were performed to analyze the ANKK1 mRNA. To study ANKK1 protein expression, we developed two polyclonal antibodies to a synthetic peptides contained in the putative Ser/Thr kinase domain.

RESULTS

We demonstrate that ANKK1 mRNA and protein were expressed in the adult central nervous system (CNS) in human and rodents, exclusively in astrocytes. Ankk1 mRNA level in mouse astrocyte cultures was upregulated by apomorphine, suggesting a potential relationship with the dopaminergic system. Developmental studies in mice showed that ANKK1 protein was ubiquitously located in radial glia in the CNS, with an mRNA expression pick around embryonic Day 15. This time expression pattern coincided with that of the Drd2 mRNA. On induction of differentiation by retinoic acid, a sequential expression was found in human neuroblastoma, where ANKK1 was expressed first, followed by that of DRD2. An opposite time expression pattern was found in rat glioma.

CONCLUSIONS

Spatial and temporal regulation of the expression of ANKK1 suggest an involvement of astroglial cells in TaqIA-related neuropsychiatric phenotypes both during development and adult life.

Neurogenetics of dopaminergic receptor supersensitivity in activation of brain reward circuitry and relapse: proposing "deprivation-amplification relapse therapy" (DART)

BACKGROUND AND HYPOTHESIS

It is well known that after prolonged abstinence, individuals who use their drug of choice experience a powerful euphoria that often precipitates relapse. While a biological explanation for this conundrum has remained elusive, we hypothesize that this clinically observed "supersensitivity" might be tied to genetic dopaminergic polymorphisms. Another therapeutic conundrum relates to the paradoxical finding that the dopaminergic agonist bromocriptine induces stronger activation of brain reward circuitry in individuals who carry the DRD2 A1 allele compared with DRD2 A2 allele carriers. Because carriers of the A1 allele relative to the A2 allele of the DRD2 gene have significantly lower D2 receptor density, a reduced sensitivity to dopamine agonist activity would be expected in the former. Thus, it is perplexing that with low D2 density there is an increase in reward sensitivity with the dopamine D2 agonist bromocriptine. Moreover, under chronic or long-term therapy with D2 agonists, such as bromocriptine, it has been shown in vitro that there is a proliferation of D2 receptors. One explanation for this relates to the demonstration that the A1 allele of the DRD2 gene is associated with increased striatal activity of L-amino acid decarboxylase, the final step in the biosynthesis of dopamine. This appears to be a protective mechanism against low receptor density and would favor the utilization of an amino acid neurotransmitter precursor like L-tyrosine for preferential synthesis of dopamine. This seems to lead to receptor proliferation to normal levels and results in significantly better treatment compliance only in A1 carriers.

PROPOSAL AND CONCLUSION

We propose that low D2 receptor density and polymorphisms of the D2 gene are associated with risk for relapse of substance abuse, including alcohol dependence, heroin craving, cocaine dependence, methamphetamine abuse, nicotine sensitization, and glucose craving. With this in mind, we suggest a putative physiological mechanism that may help to explain the enhanced sensitivity following intense acute dopaminergic D2 receptor activation: "denervation supersensitivity." Rats with unilateral depletions of neostriatal dopamine display increased sensitivity to dopamine agonists estimated to be 30 to 100 x in the 6-hydroxydopamine (6-OHDA) rotational model. Given that mild striatal dopamine D2 receptor proliferation occurs (20%-40%), it is difficult to explain the extent of behavioral supersensitivity by a simple increase in receptor density. Thus, the administration of dopamine D2 agonists would target D2 sensitization and attenuate relapse, especially in D2 receptor A1 allele carriers. This hypothesized mechanism is supported by clinical trials utilizing amino acid neurotransmitter precursors, enkephalinase, and catechol-O-methyltransferase (COMT) enzyme inhibition, which have resulted in attenuated relapse rates in reward deficiency syndrome (RDS) probands. If future translational research reveals that dopamine agonist therapy reduces relapse in RDS, it would support the proposed concept, which we term "deprivation-amplification relapse therapy" (DART). This term couples the mechanism for relapse, which is "deprivation-amplification," especially in DRD2 A1 allele carriers with natural D2 agonist therapy utilizing amino acid precursors and COMT and enkepalinase inhibition therapy.

The ANKK1 kinase gene and psychiatric disorders

The TaqIA single nucleotide polymorphism (SNP, rs1800497), which is located in the gene that codes for the putative kinase ANKK1 (ANKK1) near the termination codon of the D2 dopamine receptor gene (DRD2; chromosome 11q22-q23), is the most studied genetic variation in a broad range of psychiatric disorders and personality traits. A large number of individual genetic association studies have found that the TaqIA SNP is linked to alcoholism and antisocial traits. In addition, it has also been related to other conditions such as schizophrenia, eating disorders, and some behavioral childhood disorders. The TaqIA A1 allele is mainly associated with addictions, antisocial disorders, eating disorders, and attention-deficit/hyperactivity disorders, while the A2 allele occurs more frequently in schizophrenic and obsessive-compulsive patients. Current data show that the TaqIA polymorphism may be a marker of both DRD2 and ANKK1 genetic variants. ANKK1 would belong to a family of kinases involved in signal transduction. This raises the question of whether signaling players intervene in the pathophysiology of psychiatric disorders. Basic research on the ANKK1 protein and its putative interaction with the D2 dopamine receptor could shed light on this issue.

Cannabinoid receptors in brain: pharmacogenetics, neuropharmacology, neurotoxicology, and potential therapeutic applications

Much progress has been achieved in cannabinoid research. A major breakthrough in marijuana-cannabinoid research has been the discovery of a previously unknown but elaborate endogenous endocannabinoid system (ECS), complete with endocannabinoids and enzymes for their biosynthesis and degradation with genes encoding two distinct cannabinoid (CB1 and CB2) receptors (CBRs) that are activated by endocannabinoids, cannabinoids, and marijuana use. Physical and genetic localization of the CBR genes CNR1 and CNR2 have been mapped to chromosome 6 and 1, respectively. A number of variations in CBR genes have been associated with human disorders including osteoporosis, attention deficit hyperactivity disorder (ADHD), posttraumatic stress disorder (PTSD), drug dependency, obesity, and depression. Other family of lipid receptors including vanilloid (VR1) and lysophosphatidic acid (LPA) receptors appear to be related to the CBRs at the phylogenetic level. The ubiquitous abundance and differential distribution of the ECS in the human body and brain along with the coupling to many signal transduction pathways may explain the effects in most biological system and the myriad behavioral effects associated with smoking marijuana. The neuropharmacological and neuroprotective features of phytocannabinoids and endocannabinoid associated neurogenesis have revealed roles for the use of cannabinoids in neurodegenerative pathologies with less neurotoxicity. The remarkable progress in understanding the biological actions of marijuana and cannabinoids have provided much richer results than previously appreciated cannabinoid genomics and raised a number of critical issues on the molecular mechanisms of cannabinoid induced behavioral and biochemical alterations. These advances will allow specific therapeutic targeting of the different components of the ECS in health and disease. This review focuses on these recent advances in cannabinoid genomics and the surprising new fundamental roles that the ECS plays in the retrograde signaling associated with cannabinoid inhibition of neurotransmitter release to the genetic basis of the effects of marijuana use and pharmacotherpeutic applications and limitations. Much evidence is provided for the complex CNR1 and CNR2 gene structures and their associated regulatory elements. Thus, understanding the ECS in the human body and brain will contribute to elucidating this natural regulatory mechanism in health and disease.

Endocannabinoid receptor pharmacology

This chapter will review the basic pharmacology of endocannabinoid receptors. As the best-described cannabinoid receptors are G-protein-coupled receptors (GPCRs), those will be the focus of this chapter. We will start with a basic review of GPCR signaling, as these concepts are critical to understanding the function of cannabinoid receptors. Next, several features of cannabinoid receptor signaling will be presented, with an emphasis on the effectors modulated by cannabinoid receptors. Finally, we will finish with a discussion of cannabinoid receptor agonists and antagonists and future directions. The aim of this chapter is to introduce the cannabinoid receptor pharmacology that will be necessary to appreciate the intricacies of endocannabinoid signaling presented in later chapters.

Effects of a short-term exposure to alcohol in rats on FAAH enzyme and CB1 receptor in different brain areas

Acute alcohol exposure in rats (8% ethanol in the liquid diet for a period of 24 h) is associated with a decrease in the levels of endocannabinoids (anandamide and 2-arachidonoyl-glycerol) as well as in various N-acylethanolamines, in different brain regions. In the present study, we wanted to further explore: (i) whether these decreases might be caused by an increase in fatty acid amide hydrolase (FAAH), the enzyme involved in the degradation of N-acylethanolamines including anandamide, and (ii) whether the changes in endocannabinoid levels are accompanied by parallel changes in the major cannabinoid receptor type, the CB(1) receptor, activated by these ligands in the brain. Our data proved that FAAH activity did not increase in any of the four regions analyzed, even it was reduced in the hypothalamus and the prefrontal cortex. Paradoxically, FAAH levels increased in the hypothalamus and, to a lesser extent, in the prefrontal cortex and the amygdala, but not in the caudate-putamen. By contrast, the levels of CB(1) receptors were markedly reduced in the amygdala and prefrontal cortex of these rats, although no changes were seen in the hypothalamus and the caudate-putamen. These results suggest that reductions in the levels of endocannabinoids and related N-acylethanolamines caused by acute alcohol exposure are not originated by an enhanced degradation by FAAH enzyme, but they are associated with low levels of the receptors activated by these ligands, although this parallelism did not occur in all brain regions analyzed. In any case, these observations would support the notion of a general reduction in the activity of the cannabinoid signaling system by acute alcohol exposure.

DRD2 and ANKK1 genotype in alcohol-dependent patients with psychopathic traits: association and interaction study

BACKGROUND

The TaqI-A polymorphism of the ANKK1 gene, adjacent to the DRD2 gene, has been associated with alcoholism and other psychiatric conditions, although other DRD2 gene variants, such as the C957T polymorphism, could be related to these phenotypic traits.

AIMS

To investigate the contribution of the TaqI-A and the C957T polymorphisms to the presence of psychopathic traits in patients with alcoholism.

METHOD

We performed association and interaction analyses of the polymorphisms in 150 controls and 176 male alcohol-dependent patients assessed for the presence of dissocial personal disorder, using the Psychopathy Checklist-Revised (PCL-R).

RESULTS

There was a significant association of the TaqI-A and C957T polymorphisms when both genotypes were present, with PCL-R scores of F(1-171=0.13) (P=0.01) and a frequency of dissocial personal disorder OR=10.52, P<0.001.

CONCLUSIONS

The TaqI-A of the ANKK1 gene and the C957T of the DRD2 gene are epistatically associated with psychopathic traits in alcohol-dependent patients.

Gene expression of opioid and dopamine systems in mouse striatum: effects of CB1 receptors, age and sex

RATIONALE

Endocannabinoid, opioid, and dopamine systems interact to exhibit cannabinoid receptor neuromodulation of opioid peptides and D(4) dopamine receptor gene expression in CB(1)-cannabinoid-deficient mouse striatum.

OBJECTIVE

Using CB(1)-transgenic mice, we examine primary age-sex influences and interactions on opioid and dopamine system members' gene expression in striatum.

MATERIALS AND METHODS

Real-time quantitative polymerase chain reaction was used to analyze gene expression of opioid peptides [preproenkephalin (PPENK); preprodynorphin (PPDYN)], opioid receptors [delta-opioid receptor (delta-OR); mu-opioid receptor (micro-OR)] and dopamine receptor subtypes (D(1) through D(5)) in male/female CB(1)(+/+)/CB(1)(-/-) mice striata at two adult ages [young (60-90 days); old (140-300 days)].

RESULTS

(1) Increased PPENK and PPDYN, owing to genotype [CB(1)(+/+) vs. CB(1)(-/-)], depended on sex. When genotype-independent, they depended on sex (PPENK) or age (PPDYN). (2) delta-OR was age-dependent (higher in old). (3) micro-OR, owing to genotype, was age-dependent [higher in old CB(1)(-/-) males]. When genotype-independent, it depended on sex (higher in females). (4) Female D(1) was genotype-independent and age-dependent, while male D(1) was higher in old over young CB(1)(+/+) mice. (5) D(5), owing to genotype, was sex-dependent [higher in young female CB(1)(-/-) mice]. (6) D(2), genotype-independent, was higher in old over young male mice. (7) Young female D(3) was higher in CB(1)(-/-) over CB(1)(+/+) mice. Male D(3) was age-dependent (higher in old mice). (8) D(4), owing to genotype, was sex-dependent [higher in CB(1)(-/-) over CB(1)(+/+) females]. Genotype-independent D(4) was sex-dependent in young mice (higher in females) and age-dependent in males (higher in old).

CONCLUSIONS

Greater striatal expression is genotype-dependent in females (opioid-peptides, D(3), D(4), D(5)) and genotype-independent in both females (PPENK, mu-OR, D(4)) and old males (PPDYN, delta-OR, D(2), D(3), D(4)).

Pharmacological activation of CB1 and D2 receptors in rats: predominant role of CB1 in the increase of alcohol relapse

The classical dopamine D2 receptor has been widely studied in alcoholism. Recently, different studies have explored the role of the CB1 receptor in alcohol-related behavior. In alcohol addiction, relapse is one of the central features. In light of this, we investigated the functional roles of and interactions between CB1 and D2 receptors in alcohol relapse. We used the learned task of alcohol operant self-administration in Wistar rats. In order to evaluate alcohol relapse, we set up a protocol essentially based on the alcohol deprivation effect. We found that subchronic activation of CB1 (WIN 55,212-2, 2 mg/kg), but not D2 receptors (quinpirole, 1 mg/kg), during a period of alcohol deprivation increased long-lasting alcohol relapse. The cannabinoid-induced potentiation of alcohol relapse was mediated by a motivational and appetitive component, and not merely by alcohol consumption. This potentiation was prevented by the pharmacological inactivation of D2 receptors (raclopride, 0.1-0.3 mg/kg). Together, these results essentially demonstrate that activation of CB1 receptors plays a key role in the increase of alcohol relapse, whereas inactivation of D2 receptors modulates this aberrant behavior. We suggest that there exists a functional and interactive relationship between both receptor systems, which controls alcohol relapse and alcohol-learned tasks.

Targeted modulators of the endogenous cannabinoid system: future medications to treat addiction disorders and obesity

The endogenous endocannabinoid system encompasses a family of natural signaling lipids ("endocannabinoids") functionally related to (9)-tetrahydrocannabinol, the psychoactive ingredient of marijuana (cannabis), along with proteins that modulate the endocannabinoids, including enzymes, transporters, and receptors. The endocannabinoid system's ubiquitous regulatory actions in health and disease underscore its importance to mammalian (patho)physiology and suggest discrete targets through which it may be modulated for therapeutic gain. Medications based on the endocannabinoid system are an important focus of contemporary translational research, particularly with respect to substance abuse and obesity, two prevalent disorders with a pathogenic component of endocannabinoid system hyperactivity. Pressing health care needs have made the rational design of targeted CB1 cannabinoid-receptor modulators a promising route to future medications with significant therapeutic impact against psychobehavioral and metabolic disturbances having a reward-supported appetitive component.